Dual purpose projection screen

ABSTRACT

This application embodies a dual purpose projection screen comprising a layer of milky white, translucent, flexible plastic film, coated on one side with a layer of reflecting metal, and a layer of flexible, white opaque material covering the metal reflecting layer. This screen serves as a high gain reflection screen for rays projected against the exposed side of the translucent film, with such rays passing through said translucent film and being reflected back by the metal layer, and as a standard reflecting screen for rays projected against the exposed side of the opaque layer, with said exposed side acting as the reflecting surface for such rays. Said opaque layer also acts as a backing or strengthening layer for the screen to enhance the strength, handling and mounting of the screen on a frame. This screen can be embossed with fine lines running in the same direction in a pattern, to resemble brushed silk.

This application is a continuation in part of my application Ser. No.398,883 filed Sept. 19, 1973 for PROJECTION SCREEN, now U.S. Pat. No.3,844,644.

This invention relates to high gain, lenticular photographic projectionscreens.

The earliest projection screen was probably a wall, preferably paintedflat white. Then came the bed sheet (before the age of wild decoratorpatterns) hung over the wall now covered with flowered wallpaper. Ofcourse, stretching the bed sheet to get rid of wrinkles became the nextproblem. Ergo, there came into being a canvas screen laced and stretchedon a pipe frame.

The image has always been formed on a screen by the projector. Thus itis the final link in the optical projection chain. The white part of thepicture is formed by light projected on the screen, the dark part of thepicture, by the absence of light in the room. Obviously, the darker theroom the more contrast the picture will have.

Total darkness being difficult to achieve, even in a theater, theinventive mind set to work seeking a better screen surface; one thatwould reflect more of the projected light and retain high contrast orbetter blacks, whites and intense colors. There then came into being thefamous silver screen of Hollywood's heyday.

So we had screens in the form of a white or silver fabric stretched forflatness or a not so flat, but convenient for storage, as a roll upscreen.

The white screen was then improved by adding tiny glass beads to itssurface and this improved its "gain" or light reflecting efficiency by 2to 10 times over a matte white surface. Unfortunately, the glass beadsgive the picture a "grainy" soft focus effect; the adhesive used to holdthe beads to the fabric will oxidize in time and yellow the screen; thebeads fall off and finally being white, it is still dependent on roomdarkness for an image rich in contrast and color. As the light level inthe room increases, the image on the screen washes out.

The silver lenticular screen is the next step in the evolution ofscreens. Here a silvered surface is corrugated for the purpose ofhorizontally expanding the reflected cone of light and silvered toimprove image contrast as the ambient light level is increased. The gainof a lenticular screen is approximately 2- 4 times.

The lenticular screen manages to produce a fairly good image in a roomwith sufficient light to wash out the image on a white or beaded screen,in spite of its comparatively low gain factor which requires a higherwattage projector. However, it has two significant drawbacks (inaddition to requiring higher wattage for equivalent image brightness)and these are: The lenticular effect adds vertical lines all over theprojected image and reduces image sharpness; the screen material must bekept as flat as possible (a difficult feat with a roll-up screen).

Screens are also known in which a clear plastic film is striated on afront surface on which surface metallized reflecting coating is vacuumdeposited. The exposed surface of the deposited metallized coating isthen printed with a pigmented solution. This pigmented solution driesand forms a thin layer on which the picture is reflected. The exposedsurface of the metallized layer which forms the reflecting surface isnot as sharp as the opposite surface thereof which faithfully followsthe striations of the plastic film. The printed layer does not present aflat surface.

This brings us to the current state of the art. We know that a matte,flat surface forms the best, sharpest image (definition). We know that ahighly reflective mirror surface returns the most amount of reflectedlight (contrast) and that a lenticular effect expands the cone ofreflected light in the horizontal plane while reducing it in a verticalplane (efficiency).

Using this knowledge, the present high gain front projection screenswere developed.

It is hence an object of the present invention to obviate difficultiesencountered with previous screens.

Another object of this invention is to provide a highly improvedprojection screen material for use as a front surface projection screen.

This is a material developed for use as a front surface projectionscreen. It consists of three elements: the first being a milky whitetranslucent plastic film, the second being very fine "hairline"striations on the back surface (that which is opposite the surfacenearest to the projection source) of the film in a random pattern evenlycovering the entire surface and the third element is a highly reflectivemetallized coating (vacuum plated aluminum) on the back surface. Thepurpose of the first element is to provide a matte white surface onwhich an image can be formed by the light projected onto it from theprojection source. The fact that it is translucent rather than opaqueallows the second and third elements to function as follows. Thestriations on the back surface of the film serve to disperse thereflected cone of light in a wide horizontal angle (approximately 110°)and a narrow vertical angle (approximately 30°). The purpose of thereflective coating on the back surface is to return the rays as if thefilm were an opaque white material. The screen material can be used in anumber of different ways such as the traditional roll-up screens,grommeted along the edges and laced to a frame made of tubing orutilizing any suitable rigid frame that holds the screen on a flat panelpresenting a soft flat surface (if you push it with a finger, it dimplesand returns to flat). It is desirable that in use the screen be kept asflat as possible in order to provide an undistorted projection surface.

A further object of this invention is to provide a dual purposeprojection screen of the character described having high gain reflectingmeans on one side thereof and standard gain reflecting means on theother side thereof.

Yet a further object of this invention is to provide a projection screenof the character described which has a milky white translucent flexiblelayer exposed on one side, coated with metallized reflecting material atits other side, and a layer of white opaque flexible material bonded tothe reflecting coating.

Still a further object of this invention is to provide a screen of thecharacter described which is embossed with fine lines or grooves runningin the same direction.

A still further object of this invention is to provide a screen of thecharacter described in which said white opaque material is a matte(flat) white sheet of vinyl plastic that is bonded to the metalreflecting coating by adhesive, said vinyl layer acting to strengthenthe metal coated milky white translucent sheet in addition to providinga standard gain reflecting screen surface to the screen.

A further object of this invention is to provide a durable screen of thecharacter described which shall be inexpensive to manufacture, and whichshall yet be practical and efficient to a high degree in use.

Other objects of this invention will in part be obvious and in parthereinafter pointed out.

The invention accordingly consists in the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter described, and of which thescope of invention will be indicated in the following claims:

IN THE DRAWINGS

FIG. 1 is a greatly enlarged general view of a portion of a screen ofthis invention:

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;

FIG 3 is a schematic plan view depicting a projector with a screen ofthis invention;

FIG. 4 is a front elevational view of the projection screen of thisinvention with a frame support;

FIG. 5 is an enlarged sectional view taken along line 5--5 of FIG. 4:

FIG. 6 is a partial cross-sectional view of a modified form of screenmaterial;

FIG. 7 is a cross-sectional view of a dual purpose screen embodying amodification of the invention;

FIG. 8 is a cross-sectional view of another modified form of theinvention; and

FIG. 9 is a cross-sectional view of still another modified form of theinvention.

Referring now to FIGS. 1 and 2, there is shown the projection screengenerally designated 10. Projection screen 10 comprises a thintranslucent milky white plastic film 11 having a front surface 11a andformed on the rear surface thereof with fine parallel random striations13, and having a backing of a highly reflective metallized coating 12 onsaid striated surface. The striations may be mechanically formed by therotating action of a wire or bristle brush (not shown) moving againstand across the rear surface of the film. As can be seen, the metallizedcoating fills the fine crevices of the striations and so achieves astriated front surface 12a which faithfully follows the striations inthe film 11. The metallized coating 12 is unbacked.

Referring now to FIG. 3 there is shown the projection screen 10 infacing relationship with a projector P. The front surface 11a of theplastic film 11 first receives the image-forming light from theprojector P, which light passes through the film 11, is reflected in alenticular manner by the vertically disposed parallel striations of thefront surface 12a of the metallized coating. The image-forming light isthereby reflected back into the plastic film and carried therein duringprojection for viewing by an audience disposed in front of the screen.

The angle of viewing achieved by the projection screen is, as a resultof the lenticular effect, increased in the horizontal plane relative tothe central axis of the projector P. This expanded angle of reflectionin the horizontal plane as opposed to the vertical plane provides forgreater wide angle viewing by an audience.

Referring to FIGS. 4 and 5, there is shown, for purpose of illustration,the projection screen 10 mounted on a frame support generally shown at15. Such frame support is the one shown and described in U.S. Pat. No.3,757,479, issued Sept. 11, l973.

The frame shown in the drawing is rectangular in shape, with the majordimension being along the horizontal plane. Said frame has an outertransverse wall 20 from which two flanges 21, 22 extend in parallelrelation. Flange 21 will be at the rear of the frame 15 while flange 22will be at the front of the frame. Extending outwardly from transversewall 20 is a wall 23 aligned with flange 21, and a wall 24 aligned withflange 22. Between walls 23, 24 is formed a groove 25 having sideundercuts 26 to provide overhang portions 27 extending from walls 23, 24overlying the groove. At the bottom of groove 25 (or at top oftransverse wall 20) is a wide V-shaped surface formed with inclinedcovering surface portions 30 meeting in a longitudinal apex 31. Theundercuts 26 are semi-cylindrical in shape and merge with the inclinedsurfaces 30. Extending from wall 24 is an overhang ledge 32.

Strip 33 for attaching screen 10 to frame 15, is made of flexible,resilient compressible synthetic plastic or rubber. Said strip is asingle continuous strip of proper length to go all around the frame.

Wings 40 of said flexible strip 33 will press the film down intosurfaces 30 and into contact with the internal undercut surfaces 26. Thestrip then has a toggle action and cannot become loose because to comeout of the groove, the strip 33 would have to substantially increase inwidth as the strip flattens. Also it should be noted that the normalwidth of the strip when fully in the groove, as shown in FIG. 5, is notcompressed would be greater than the normal width, when the strip is notin the groove. This is so because the strip is flatter when in thegroove than in normal unflexed inverted V-shape. The flatter the stripis, the wider it is. Hence the strip is in compression because it isflatter in the groove than when it is in normal unconstricted condition.The shallower inclined surfaces 30 prevent the strip from becomingnarrower and prevent increasing its angularity when in the groove. Thefront surface 11a of the screen faces the projector P. The part of thescreen stretched by the frame provides a flat soft panel as shown at thetop of FIG. 5, between the ledges 32 of the frame.

It has been found that the translucent plastic film 11 having a degreeof light transmission of from about 60 percent to about 75 percent, whenbacked with a highly reflective metallized coating, provides a suitableprojection screen.

The degree of light transmission is determined by situating a lightsource at a fixed distance from a photometer and measuring theluminescence. This first measurement is considered a 100 percent degreeof transmission insofar as there is no interposed medium, save for theambient air, so as to diminish the illumination. Then a translucentplastic film is placed at a specific distance between the aforesaidlight source and photometer, and a second reading is taken of theluminescence registered by the photometer. Then a ratio is calculated ofthe degree of light transmission. Obviously an opaque film would give azero degree of light transmission.

It has been further found that when the light transmission percentagedecreases to below about 60 percent, the degree of reflectivity from themetal backing is diminished to a point wherein the screen cannot be saidto be suitably operable. At the higher side of the scale, when thedegree of light transmission exceeds about 75 percent there is noticedthat while the reflectivity is high, there is a significant loss in thepicture forming qualities of the film. A transparent film employed as ascreen would not be operable, as such, but would be in effect a mirrormerely reflecting the image rather than retaining the image forprojection. Further at the high degrees of light transmission"hot-spots" are formed in the film.

The translucent plastic films useful according to this invention may bepolyesters, such as Melinex Type 337, manufactured by ICI America, Inc.("Melinex" is a trademark of ICI America, Inc.); Type EB-11 Mylar,manufactured by E. I. Dupont de Nemours, Inc. ("Mylar" is a registeredtrademark of E. I. Dupont de Nemours Wilmington, Del.); polyvinyls, suchas Type 100 BG 15 UW Tedlar, manufactured by E. I. Dupont de Nemours,("Tedlar" is a trademark of E. I. Dupont de Nemours, Wilmington, Del.);polyamides such as nylon; and the like.

The plastic film thickness may vary and is not narrowly critical.Polymeric film thickness of from about 0.001 inch to about 0.005 inchare found suitable for the plastic film 11.

The translucent plastic film may be formed by a clear polymer havingfinely divided, evenly dispensed particulates or pigments. Preferredpigmenting agents are those which provide a milky-white apperance in theformed plastic film. The particulates or pigmenting agents may beincorporated in the film in thermoforming a thermoplastic film.

Suitable reflective backing for coating the one plastic film surface,includes metallized backing such as aluminum and the like. The aluminummay be vacuum deposited on the striated surface of the plastic film.

The striations are formed in the one surface of the plastic film byusing a wire or bristle rotating brush. The brush is rotated in relationto the plastic film and moved across the film so that the striations arefine and generally randomly parallel in the vertical direction.

Although the projection screen 10 of this invention may, as stated, bemounted to a frame such as the one described above, it also may beutilized in the conventional roll-up screens grommeted along the edgesand laced to a frame made of tubing or mounted in any other way so thatthe front surface 11a of the film 11 faces the projector and presents asoft panel. In use, it is desirable that the screen be kept as flat aspossible in order to provide an undistorted projection surface. In anyevent, the front surface of the screen panel faces the projector in useas a screen.

The terms "horizontal"and "vertical" as used hereinbefore andhereinafter throughout the specification refer to orientations of thescreen surface for convenient and conventional viewing by an audiencedistribution extending more horizontally than vertically. Therefore inFIG. 3 the plan view depicts the horizontal extent of the screen and theangle of viewing is along the horizontal plane.

In FIG. 6 there is shown a piece of screen material 10a illustrating amodified construction. Said piece of screening material 10a comprises amilky white translucent plastic layer or film 50 laminated to a plasticlayer or film 51 which may be clear. The layer 50 has a front flatsurface 50a which receives the photographic rays from a photographicprojector.

The rear surface of layer 51 is scratched or striated randomly up anddown and said surface is covered by vacuum deposited reflective metalsuch as aluminum. The coating 52 is unbacked. This screen 10a may beused like screen 10 as described above.

The screen 10 can be rigid and self supporting and the metallizedreflecting coating could be vacuum deposited with the screen in concaveshape, to contrast the reflected cone of light. Also the screen 10 couldbe adhered to a concave rigid supporting surface if desired.

It will be understood that if desired, the striations may be omittedfrom the above described screens.

Referring now to FIG. 7, there is shown a screen 60 comprising a layerof film 61 of milky white translucent plastic material similar tomaterial 11 described hereinabove.

Applied to the rear surface of said layer 61 is a layer or coating 62 ofreflecting metal, such as aluminum. This reflecting layer can be vacuumdeposited or otherwise applied. Bonded to the rear surface of layer 62as by an adhesive layer 63 is a sheet or layer 64, of flexible, opaque,matte (flat) white vinyl or other suitable opaque plastics or othermaterial.

Layers 61, 62 are flexible. The sheet or layer 64 is also flexible andacts as a strengthening backing for layers 61, 62. The layers 61, 62 actas a high gain reflecting screen similar to layers 11, 12 of screen 10hereinabove. In addition, rays can be projected onto the exposed side oflayer 64 to provide a standard gain screen reflecting surface. Thuslayer 64 has two functions. It strengthens the screen layers 61, 62 andit provides an additional standard screen surface to the high gainscreen constituting layers 61, 62.

Screen layers 61, 62 can be embossed as between corrugated pressurerollers, with fine lines which are substantially straight and parallelto produce a brushed silk or striated effect. The lines could be in apattern of very fine lines which could be about 0.004" or 0.005" deep,and such lines could be about 0.010" apart. The lines could be ofdifferent lengths or run entirely through the screen all running invertical directions.

In FIG. 8 the screen 70 comprises a layer or film 71 of flexible milkywhite translucent plastic film or other material coated with a layer 72of reflecting metal to which a layer 73 of flexible, white, matte (flat)opaque plastic such as vinyl, is bonded by adhesive or otherwise. Thisscreen 70 functions like screen 60 but does not have embossed striationsfor lenticular effect but it may have brushed striations.

In FIG. 9 there is shown a screen 80 comprising a milky whitetranslucent flexible film, layer or sheet 81 scratched as by brushing.

Vacuum deposited or otherwise applied to said scratched surface, is alayer 82 of reflecting metal to which is bonded, as by a thin layer 83of adhesive, a sheet or layer 84 of flexible opaque, matte white vinylor other plastic or other material.

The bonding of the opaque layer to the metal layer, may be accomplishedwith heat sensitive adhesive, microscopic or about 0.0005" in thickness.

The layers 61, 62 are wavy on both sides. The opaque white layer couldbe between 0.005" to 0.020" in thickness.

The matte (flat) white surface of layers 64, 73, 80 can be achieved bythe vinyl sheet itself or by a coating of ink or paint compatible withthe vinyl sheet.

The screens 60, 70 or 80 can be mounted on a suitable frame such as 15shown herein or on a frame that can be turned around to bring eitherside toward the projector so that either side of any of said screens canbe reflectively projected upon.

It will be easy to note which side is the high gain side and which isthe standard side of screens 60, 70 or 80 since the high gain side willhave a dull metal appearance, because the reflecting metal will showthrough the milky white translucent layer which is light transmitting,and the standard side is flat white and opaque.

It will thus be seen that there is provided an article in which theseveral objects of this invention are achieved, and which is welladapted to meet the conditions of practical use.

As possible embodiments might be made of the above invention, and asvarious changes might be made in the embodiments above set forth, it isto be understood that all matter herein set forth or shown in theaccompanying drawings, is to be interpreted as illustrative only.

I claim:
 1. A dual purpose photographic front projection screencomprising a milky white, translucent, flexible, plastic film having afront, surface to face a projection source, a reflective metal layer onthe opposite surface of said film, said film allowing projected rays topass through said film to be reflected back through the film by thesurface of said metal layer adjacent said plastic film, and said filmalso carrying the image caused by rays passing therethrough while therays are projected onto said front surface of said film, and a layer offlexible opaque reflective material bonded to the surface of the metallayer remote from said film, said opaque layer providing a strengtheningbacking for said film and metal layer, and presenting an exposed sideserving as a reflecting surface for images projected onto said exposedside of said opaque layer.
 2. The combination of claim 1, said opaquelayer being white.
 3. The combination of claim 1, said opaque layercomprising vinyl.
 4. The combination of claim 1, said opaque layercomprising matte white plastics material.
 5. The combination of claim 1,said film being embossed with parallel grooves running substantially inthe same direction.
 6. The combination of claim 1, said metal layerbeing vacuum deposited on said opposite side of said film.
 7. Thecombination of claim 1, said film being provided with striations on saidopposite side thereof, and said metal layer covering said striations. 8.A dual purpose photographic front projection screen comprising a milkywhite, translucent, flexible, plastic film having one surface to face aprojection source, a reflective metal layer on the opposite surface ofsaid film, said film allowing projected rays to pass through said filmto be reflected back through the film by the surface of said metal layeradjacent said plastic film, and said film also carrying the image causedby rays passing therethrough while the rays are projected onto said onesurface of said film, and a layer of flexible opaque material bonded tothe surface of the metal layer remote from said film, said opaque layerproviding a strengthening backing for said film and metal layer, andpresenting an exposed side serving as a reflecting surface for imagesprojected onto said exposed side of said opaque layer, said film beingprovided with striations on said opposite side thereof, and said metallayer covering said striations, said metal reflecting layer comprisingreflecting metal vacuum deposited on said striated side of said film. 9.The combination of claim 8, said opaque layer being white.
 10. Thecombination of claim 8, said opaque layer comprising vinyl.
 11. Thecombination of claim 8, said opaque layer comprising matte whiteplastics material.